RP consists to first order of 3 SSA components that together amount to more than 85% of the total signal variance [1]}: the [2]} drift, the [3]}, [4]} free oscillation (actually a double component with periods \(\sim \) 433 and \(\sim \) 434 days), and the forced annual oscillation. Polar drift does not have a universally accepted explanation [5]}, [6]}, [7]}, [8]}. The two other oscillatory components (Chandler and annual) are obtained using the Liouville-Euler system, that describes the motion of a spherical rotating solid body (e.g. [9]}, chapter 3, system 3.2.9).
